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At least 1,027 records · Page 57

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NASA NTRS1991

A method for the construction of a lunar transfer trajectory using ballistic capture

The weak stability boundary (WSB) method for the design and optimization of lunar transfer trajectories is described. Considerable savings of propellant are shown over classical methods of orbit transfer such as the Hohmann transfer method. The savings in Delta V required of the spacecraft ranges from 100 to 200 m/s, which translates into a 5-10 percent reduction in spacecraft propellant for a science payload. Another advantage of the WSB method involves the utilization of low thrust propellant systems. Since the transfer trajectory is nearly completely ballistic, thrusting propulsive maneuvers may be performed over a long time duration.

Miller, James K.↗

NASA NTRS1993

Nonsmooth trajectory optimization - An approach using continuous simulated annealing

An account is given of the properties of a continuous simulated annealing algorithm that can function as a global optimization tool for nonsmooth dynamic systems, as shown in the case of a trajectory-optimization program implementation. The approach is shown to successfully solve the problem of nonsmooth trajectory optimization for a high performance rigid-body aircraft. The results obtained demonstrate the superiority of the simulated annealing algorithm over widely used algorithms.

Lu, Ping↗

NASA NTRS1993

Minimum-fuel trajectories for hypersonic vehicles with aeropropulsive interactions

The class of hypersonic vehicle configurations with single stage-to-orbit (SSTO) capability reflect highly integrated airframe and propulsion systems. These designs are also known to exhibit a large degree of interaction between the airframe and engine dynamics. Consequently, even simplified hypersonic models are characterized by tightly coupled nonlinear equations of motion. It is to be determined how these features, along with the stringent mission requirements placed on the vehicle, affect its trajectory performance. In this paper, a trajectory optimization problem for a generic hypersonic lifting body will be formulated, a solution method outlined, and results presented. The solution sought is a minimum-fuel trajectorv for orbit injection. It is also desired to study the effect of heating constraints on the vehicle.

Lovell, T. A.↗

NASA NTRS1993

Inverse dynamics: Simultaneous trajectory tracking and vibration reduction with distributed actuators

This paper addresses the problem of inverse dynamics for articulated flexible structures with both lumped and distributed actuators. This problem arises, for example, in the combined vibration minimization and trajectory control of space robots and structures. A new inverse dynamics scheme for computing the nominal lumped and distributed inputs for tracking a prescribed trajectory is given.

Devasia, Santosh↗

NASA NTRS1994

A genetic technique for planning a control sequence to navigate the state space with a quasi-minimum-cost output trajectory for a non-linear multi-dimnensional system

There are many multi-stage optimization problems that are not easily solved through any known direct method when the stages are coupled. For instance, we have investigated the problem of planning a vehicle's control sequence to negotiate obstacles and reach a goal in minimum time. The vehicle has a known mass, and the controlling forces have finite limits. We have developed a technique that finds admissible control trajectories which tend to minimize the vehicle's transit time through the obstacle field. The immediate applications is that of a space robot which must rapidly traverse around 2-or-3 dimensional structures via application of a rotating thruster or non-rotating on-off for such vehicles is located at the Marshall Space Flight Center in Huntsville Alabama. However, it appears that the development method is applicable to a general set of optimization problems in which the cost function and the multi-dimensional multi-state system can be any nonlinear functions, which are continuous in the operating regions. Other applications included the planning of optimal navigation pathways through a transversability graph; the planning of control input for under-water maneuvering vehicles which have complex control state-space relationships; the planning of control sequences for milling and manufacturing robots; the planning of control and trajectories for automated delivery vehicles; and the optimization and athletic training in slalom sports.

Hein, C.↗

NASA NTRS1992

Minimum-exposure near-terrain flight trajectories for rotorcraft

The paper presents methodologies for constructing optimal trajectories for rotorcraft executing nap-of-the-earth flight over known terrain. Unlike the standard techniques, the present approaches require only a one-dimensional numerical search for determining optimal trajectories. Numerical algorithms are developed using two kinematic vehicle models in conjunction with optimal control theory.

Menon, P. K. A.↗

NASA NTRS1994

A trajectory modeling investigation of the biomass burning-tropical ozone relationship

The hypothesis that tropical total O3 maxima seen by the TOMS satellite derive from African biomass burning has been tested using isentropic trajectory analyses with global meteorological data fields. Two case studies from the 1989 biomass burning season demonstrate that a large fraction of the air arriving at the location of TOMS O3 maxima passed over regions of intense burning. Other trajectories initiated at a series of points over Africa and the Atlantic suggest flight strategies for field studies to be conducted in September 1992.

Pickering, Kenneth E.↗

NASA NTRS1994

Trajectory analysis of Polar Patrol Balloon (PPB) flights in the stratosphere over Antarctica in summer and spring: A preliminary result

Actual trajectories of two PPB's which flew in the Antarctic stratosphere in austral summer and spring are compared with those calculated based on objective analysis data of Japan Meteorological Agency (JMA). The differences between the actual and calculated trajectories are discussed to check reliability of the JMA objective analysis data for the stratosphere, and to detect subsynoptic scale variability due to gravity waves and others.

Kanzawa, Hiroshi↗

NASA NTRS1994

Hierarchical Control and Trajectory Planning

Most of the time on this project was spent on the trajectory planning problem. The construction is equivalent to the classical spline construction in the case that the system matrix is nilpotent. If the dimension of the system is n then the spline of degree 2n-1 is constructed. This gives a new approach to the construction of splines that is more efficient than the usual construction and at the same time allows the construction of a much larger class of splines. All known classes of splines are reconstructed using the approach of linear control theory. As a numerical analysis tool control theory gives a very good tool for constructing splines. However, for the purposes of trajectory planning it is quite another story. Enclosed in this document are four reports done under this grant.

Martin, Clyde F.↗

NASA NTRS1993

Interpretation of NO(x)/NO(y) observations from AASE-2 using a model of chemistry along trajectories

In situ measurements of NO and NO(y) are used to derive the ratio NO(x)/NO(y) along the flight track of the NASA ER-2 aircraft. Data are presented for two flights at midlatitudes in October 1991 during the Airborne Arctic Stratospheric Expedition-2 (AASE-2). Aerosol particle surface area was concurrently measured. The observations are compared with a photochemical model integrated along back trajectories from the aircraft flight track. Comparison of observations with the model run along trajectories and at a fixed position clearly and quantitatively demonstrates the importance of an air parcel's dynamic history in interpretation of local chemical observations. Comparison of the data with model runs under different assumptions regarding heterogeneous chemistry further reinforces the case for occurrence of the reaction of N2O5 + H2O on sulfate aerosol surfaces in the atmosphere. Finally, comparisons for which relative changes in the model and the data are not consistent caution that our ability to resolve all the observations is not yet complete.

Kawa, S. R.↗

NASA NTRS1994

Minimum fuel lunar trajectories for a low-thrust power-limited spacecraft

Minimum fuel trajectories from a low Earth parking orbit to a low Moon orbit are obtained for a low-thrust power-limited spacecraft with thrust acceleration levels of the order of 10(exp -3) G. The trajectories are found by matching an Earth spiral to a Moon spirit at some intermediate distance. Results are given for the planar case and for the three dimensional case where the Moon orbit is polar.

Golan, Oded M.↗

NASA NTRS1996

Experimental and Theoretical Results in Output-Trajectory Redesign for Flexible Structures

In this paper we study the optimal redesign of output trajectory for linear invertible systems. This is particularly important for tracking control of flexible structures because the input-state trajectories that achieve the required output may cause excessive vibrations in the structure. A trade-off is then required between tracking and vibrations reduction. We pose and solve this problem as the minimization of a quadratic cost function. The theory is developed and applied to the output tracking of a flexible structure and experimental results are presented.

Dewey, J. S.↗

NASA NTRS1997

Optimal Trajectories for the Helicopter in One-Engine-Inoperative Terminal-Area Operations

This paper presents a summary of a series of recent analytical studies conducted to investigate one-engine-inoperative (OEI) optimal control strategies and the associated optimal trajectories for a twin engine helicopter in Category-A terminal-area operations. These studies also examine the associated heliport size requirements and the maximum gross weight capability of the helicopter. Using an eight states, two controls, augmented point-mass model representative of the study helicopter, continued takeoff (CTO), rejected takeoff (RTO), balked landing (BL), and continued landing (CL) are investigated for both vertical-takeoff-and-landing (VTOL) and short-takeoff-and-landing (STOL) terminal-area operations. The formulation of the non-linear optimal control problems with considerations for realistic constraints, solution methods for the two-point boundary-value problem, a new real-time generation method for the optimal OEI trajectories, and the main results of this series of trajector optimization studies are presented. In particular, a new balanced-weight concept for determining the takeoff decision point for VTOL Category-A operations is proposed, extending the balanced-field length concept used for STOL operations.

Chen, Robert T. N.↗

NASA NTRS1996

Trajectory Optimization of an Interstellar Mission Using Solar Electric Propulsion

This paper presents several mission designs for heliospheric boundary exploration using spacecraft with low-thrust ion engines as the primary mode of propulsion The mission design goal is to transfer a 200-kg spacecraft to the heliospheric boundary in minimum time. The mission design is a combined trajectory and propulsion system optimization problem. Trajectory design variables include launch date, launch energy, burn and coast arc switch times, thrust steering direction, and planetary flyby conditions. Propulsion system design parameters include input power and specific impulse. Both SEP and NEP spacecraft arc considered and a wide range of launch vehicle options are investigated. Numerical results are presented and comparisons with the all chemical heliospheric missions from Ref 9 are made.

Kluever, Craig A.↗

NASA NTRS1998

Optimization of Supersonic Transport Trajectories

This paper develops a near-optimal guidance law for generating minimum fuel, time, or cost fixed-range trajectories for supersonic transport aircraft. The approach uses a choice of new state variables along with singular perturbation techniques to time-scale decouple the dynamic equations into multiple equations of single order (second order for the fast dynamics). Application of the maximum principle to each of the decoupled equations, as opposed to application to the original coupled equations, avoids the two point boundary value problem and transforms the problem from one of a functional optimization to one of multiple function optimizations. It is shown that such an approach produces well known aircraft performance results such as minimizing the Brequet factor for minimum fuel consumption and the energy climb path. Furthermore, the new state variables produce a consistent calculation of flight path angle along the trajectory, eliminating one of the deficiencies in the traditional energy state approximation. In addition, jumps in the energy climb path are smoothed out by integration of the original dynamic equations at constant load factor. Numerical results performed for a supersonic transport design show that a pushover dive followed by a pullout at nominal load factors are sufficient maneuvers to smooth the jump.

Ardema, Mark D.↗

NASA NTRS1998

Development of Advanced Methods of Structural and Trajectory Analysis for Transport Aircraft

Ardema, Mark D.↗

NASA NTRS1999

Janus Trajectory Design

The proposed Janus Discovery Class mission will pass over opposite illuminated hemispheres of the planet Mercury on two successive flybys and will pass over a crater near Mercury's South geographic pole on the third and Final flyby. Three probes will be released by the main spacecraft prior to the first Mercury flyby to pass over Mercury's geographic poles and over the anti-Sunward side. The science team wanted to complete the first Mercury flyby within approximately 110 days of launch and the second Mercury flyby within approximately 365 days of launch. A direct trajectory was chosen which met the basic constraints of the science team while meeting the Discovery launch vehicle constraints. The objective of this paper is to serve as an overview of the Janus trajectory design. The proposal submitted in June 1998 provides a comprehensive overview of the Janus mission.

Marr, Gregory C.↗

NASA NTRS1999

Janus Trajectory Design

The proposed Janus Discovery Class mission will pass over opposite illuminated hemispheres of the planet Mercury on two successive flybys and will pass over a crater near Mercury's South geographic pole on the third and final flyby. Three probes will be released by the main spacecraft prior to the first Mercury flyby to pass over Mercury's geographic poles and over the anti-Sunward side. The science team wanted to complete the first Mercury flyby within approximately 110 days of launch and the second Mercury flyby within approximately 365 days of launch. A direct trajectory was chosen which met the basic constraints of the science team while meeting the Discovery launch vehicle constraints. The objective of this paper is to serve as an overview of the Janus trajectory design. The proposal submitted in June 1998 provides a comprehensive overview of the Janus mission.

Marr, Gregory C.↗